Presently, tau-targeting therapies to treat Alzheimer's disease (AD) are limited by efficacy and safety. To date, the majority of therapeutic trials have focused on A? because of the strong genetic evidence linking mutations in APP and presenilins to familial AD. However, tau-based neurofibrillary tangle (NFT) pathology correlates more closely with cognitive decline than A? plaques. Therefore, targeting AD's NFT pathology may prove to be a complimentary, alternative strategy to A? directed AD therapies, which up to this point have been generally unsuccessful. Thus, the long-term goal of this work is to gain a better understanding of the cellular mechanisms of NFT clearance in order to develop more effective therapies. The overall objective of this proposal is to dissect the multiple roles of transcription factor EB (TFEB), a critical regulator of lysosomal biogenesis, in clearing pathological forms of tau. The central hypothesis is that astroglial TFEB expression enhances uptake and clearance of aberrant extracellular tau, preventing the neuronal spreading of tau pathology, in addition to TFEB's cell-autonomous effect in enhancing the autophagy-lysosomal pathway (ALP). This hypothesis has been formulated based on recent work demonstrating the therapeutic potential of TFEB in ameliorating tau pathology in a mouse model of tauopathy. In addition, TFEB is known to upregulate endocytosis genes and enhance macropinocytosis of protein aggregates. With studies demonstrating the existence of extracellular tau and cell-to-cell tau spreading, targeting extracellular tau will likely prove crucial to halting disease progression. Thus, through TFEB-mediated enhancement of uptake mechanisms and the ALP, astrocytes are prime candidates to take up and clear pathologic extracellular tau, reducing overall tau pathology and preventing further seeding of aggregation and spreading. In order to accomplish the overall objective for the current proposal, the central hypothesis will be tested by pursuing the following specific aims: 1) Determine the mechanistic effect of TFEB on tau handling by astrocytes in vitro through measuring TFEB- mediated astrocyte uptake and clearance of synthetic tau aggregates and soluble tau. 2) Determine the effect of astroglial TFEB on tau pathology in vivo via astrocyte-specific TFEB overexpression in tauopathy mouse models. Changes in overall tau pathology and cognitive behavior will be assessed, in addition to the impact on the propagation of NFT-like neuronal tau pathology. The successful completion of these aims will define the extracellular mechanisms of TFEB's action and provide valuable insight into the poorly defined role of astrocytes in tauopathies. Clarification of the extracellular mechanisms of TFEB-mediated pTau clearance is expected to identify novel therapeutic targets to guide the development of new therapeutic strategies in the treatment of AD.